1. Field of the Invention
The present invention relates to a medical instrument for the removal of deposits formed on the inner walls of the arteries or veins, comprising an outer tube fixed to the end of a flexible tube or sheath intended to be introduced into the artery or the vein, an inner tube displaceable longitudinally in the outer tube, this inner tube being equipped, at its distal end, with a convex head exhibiting an axial passage continuing the inner tube, extensible cutting and scraping means, and means for ensuring the expansion and retraction of the cutting and scraping means under the effect of the relative longitudinal displacement of the two tubes.
2. Description of Prior Art
In the U.S. Pat. No. 5,074,871 an instrument of this type is described, in which the cutting and scraping means consist of flexible arms, the ends of which are articulated, on the one hand, on the integral convex head of the inner tube, and, on the other hand, on the end of the outer tube. When the convex head is brought near the end of the outer tube, the flexible arms deflect by buckling in such a way that an expansion of the cutting device is obtained. In the median part of some of the arms there is additionally cut out an aggressive tongue, which constitutes the actual cutting means. The retraction of the flexible arms is ensured by their inherent elasticity, as well as by the displacement in the opposite direction of the head. This head has an axial hole permitting the passage of a guide wire or of a catheter for inflating a balloon. Bearing in mind that, in accordance with the standards nowadays set down in surgery, the diameter of the introducer must not exceed 3 mm, so that the instrument has to have a diameter substantially less than 3 mm (in order to be able to staunch the blood), it is possible to appreciate the small dimensions of the hinge pins of the flexible blades and, consequently, the fragility of these hinges. Not only are the flexible blades and their attachments to the head and to the outer tube very fragile, but the problem of removing the material torn from the wall of the blood vessel has not been solved. It is proposed, in said document, to withdraw the material torn off by means of a catheter equipped with a balloon or a membrane surrounding the cutting head formed by the flexible arms. In both cases, the removal of the material torn off is by no means guaranteed, and, instead, there is a risk of a substantial quantity of material being entrained in the blood flow.
From the U.S. Pat. No. 4,794,928, an angioplasty instrument is also known, which comprises a catheter and expandable cutting means consisting of blades. These blades are either articulated on a support and controlled by cams, or consist of elastic arms which are spaced apart by the inflation of a balloon. No means is proposed for holding and removing the material torn off from the wall of the blood vessel.
The Patent DE 38 30 704 describes an instrument in which blades of a shell shape are mounted on a support made of elastically deformable material, the deformation of which, by means of a traction wire, provides for the expansion of the shells.
It has also been proposed to mount rigid blades at the end of a catheter and to control the spacing of these blades by means of a wire acting on connecting rods articulated at an intermediate point of the blades. Such a mechanism is not only fragile, given the small dimensions in which it has to be made, but it is in addition mechanically disadvantageous on account of the ratio of the forces present. In particular, when the blades, which are spaced apart, have scraped off a certain quantity of material, it is no longer possible in practice to close the blades. In addition, the problem of removing the material torn off from the wall of the blood vessel has not been solved. Furthermore, it is not possible in practice to have an inner tube for the injection of a liquid.